1. Field of the Invention
The present invention, generally, relates to motor control systems and, more particularly, to a technique for effectively functioning as an online monitor of the performance of a direct current motor and for performing an online diagnosis of any fault detected before participating in a shutdown procedure.
2. Description of the Prior Art
By carefully studying the types of the failures that occur in a direct current motor driven mechanism, particularly as used in a printer for a computer system, it is possible to develop a list of those operations that should be monitored. The monitoring of such operations can reveal conditions or problems that lead to failures, and past efforts have all caused system shutdown before such failures occur.
Clearly, a system shutdown is preferable, when compared with a system failure. However, it has been found that a system shutdown can cause a problem in diagnosing the cause and, therefore, in providing the necessary preventive maintenance, because all too often it is an input data error that caused the shutdown and not a fault with the system. Therefore, what is needed is a way to diagnose the situation before the system shutdown procedure is initiated.
A U.S. Pat. No. 4,733,343 to Yoneda et al. describes a trouble identification scheme in connection with a numerical control machine, so that the machine may be stopped with a controlled "slow-down". Once stopped, however, repair of the trouble is not provided for.
In a Federico et al. U.S. Pat. No. 4,514,846 that issued in 1985, there is described a way of isolating the detected fault to a particular control board for later study and, hopefully, diagnosis of the cause. These inventors recognize that it is difficult to diagnose the cause of a fault at a later time, and so, there is provided this system of isolating a fault to a particular control board as a way of developing a history of where the faults are occurring.
There is a U.S. Pat. No. 4,179,732 that issued in 1979 to Khan et al. which also recognizes the clear advantages of having the diagnosis function performed, but it teaches that it must be done off-line. See column 11, lines 20-29. This teaching is a self diagnostic capability in printer microprocessor architecture that is done after the function is terminated and the printer system is driven off-line.
Of the U.S. patents assigned to the same Assignee as the present invention, U.S. Pat. No. 4,287,461; U.S. Pat. No. 4,452,136; U.S. Pat. No. 4,570,110; and U.S. Pat. No. 4,591,969 concern various aspects of motor control systems. However, of these prior patents, only the '136 patent teaches the use of a diagnostic capability, but that is an off-line arrangement. A printer control microprocessor is described as containing a diagnosis capability that is selected manually and executed off-line. See column 6, line 45 to column 7, line 5.
In U.S Pat. No. 4,730,164 to Daido et al., a diagnosis routine is described for detecting an abnormal condition in a stepping motor, but it must be done at initialization only, that is, before the control routine is applied. In this arrangement, there is no monitoring available during operation for a fault that can develop then.
As described previously above, what is needed is a technique for monitoring a system during operations and for diagnosing a fault before the system is shut down. It is to this end that the present invention is directed. Moreover, when the present invention is used as it will be described, it provides other advantages not available and not even contemplated by the prior arrangements.